Ammonia-Induced Restructuring of Iron Single-Crystal Surfaces

AMMONIA-INDUCED RESTRUCTURING OF IRON SINGLE-CRYSTAL SURFACES 

This section presents research which studied the effects of ammonia inducing restructuring on the ammonia synthesis activity of Fe(llO), Fe(lOO), and 

Fe(lll) surfaces. Also, the effects of the ammonia pretreatment on iron surfaces with coadsorbed potassium and aluminum oxide are presented. 

Clean Iron Single Crystals Pretreated with Ammonia Prior to Ammonia Synthesis 

Rates of ammonia synthesis over initially clean (110), (100), and (111) faces of iron are shown in Fig. 4.28, along with the rates obtained after the treatment of the Fe(llO), Fe(lOO), and Fe(lll) crystals with 5 torr of ammonia at 723 K for 30 minutes prior to the ammonia synthesis reaction. The Fe(llO) and Fe(lOO) surfaces show large increases in activity for ammonia synthesis (Fig. 4.28) after ammonia pretreatment. The initially inactive Fe(llO) face becomes about half as active as the clean Fe(l 11) surface. The activity of the Fe(lOO) surface, for ammonia synthesis, increases by a factor of four and the Fe(lll) surface shows only a small decrease in activity after ammonia pretreatment. Scanning electron micrographs of the ammonia pretreated iron single-crystal surfaces are shown in Fig. 4.29. They clearly show that ammonia pretreatment drastically changes the surface structure of the (110), (100), and (111) faces of iron. 

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